Molecular Signaling Mechanisms for the Antidepressant Effects of NLX-101, a Selective Cortical 5-HT1A Receptor Biased Agonist

Abstract

Depression is the most prevalent of the mental illnesses and serotonin (5-hydroxytryptamine, 5-HT) is considered to be the major neurotransmitter involved in its etiology and treatment. In this context, 5-HT_1A receptors have attracted interest as targets for therapeutic intervention. Notably the activation of presynaptic 5-HT_1A autoreceptors delays antidepressant effects whereas the stimulation of postsynaptic 5-HT_1A heteroreceptors is needed for an antidepressant action. NLX-101 (also known as F15599) is a selective biased agonist which exhibits preferred activation of cortical over brain stem 5-HT_1A receptors. Here, we used behavioral, neurochemical and molecular methods to examine the antidepressant-like effects in rats of a single dose of NLX-101 (0.16 mg/kg, i.p.). NLX-101 reduced immobility in the forced swim test when measured 30 min but not 24 h after drug administration. NLX-101 increased extracellular concentrations of glutamate and dopamine in the medial prefrontal cortex, but no changes were detected in the efflux of noradrenaline or 5-HT. NLX-101 also produced an increase in the activation of pmTOR, pERK1/2 and pAkt, and the expression of PSD95 and GluA1, which may contribute to its rapid antidepressant action.

Keywords: Akt; BDNF; ERK1/2; GluA1; dopamine; glutamate; mTOR; medial prefrontal cortex; p11.

Figure 1

Antidepressant-like action of NLX-101 in the forced swim test (FST) conducted 30 min (a), 24 h (b) and 7 days (c) after the intraperitoneal injection of 0.16 mg/kg of NLX-101. Results are expressed as mean ± SEM of n = 5–6 rats/group, * p < 0.05, two-tailed Student’s t-test.

Figure 2

Behavioral response in the open field test (OFT). Locomotor activity after the administration of 0.16 mg/kg of NLX-101 is expressed as distance traveled in meters during 10 min. Results are expressed as mean ± SEM of n = 5–6 rats per group.

Figure 3

Effects of the administration of 0.16 mg/kg of NLX-101 or vehicle (arrow) on the extracellular concentration of noradrenaline (a), serotonin (b), dopamine (c) and glutamate (d) in the mPFC. Data (mean ± SEM) are expressed as percentage changes in the four basal pretreatment values. Number of animals is indicated in parentheses. * p < 0.05 and ** p < 0.0005 different from the corresponding vehicle group, Tukey’s multiple comparison test following significant two-way repeated measures ANOVA.

Figure 4

Effects of NLX-101 (0.16 mg/kg) and vehicle (Veh) on the concentration of pmTOR (a) and pERK1/2 (b) in the prefrontal cortex at 30 min, 1 h, 2 h and 6 h after its intraperitoneal administration. Results are expressed as mean ± SEM. Number of animals is indicated within the bars. * p < 0.05 compared with the corresponding vehicle group (two-tailed Student’s t-test).

Figure 5

Effects of NLX-101 (0.16 mg/kg) and vehicle (Veh) on the concentration of postsynaptic proteins p11 (a) and PSD95 (b) in the prefrontal cortex at 30 min, 1 h, 2 h and 6 h after its intraperitoneal administration. Results are expressed as mean ± SEM. Number of animals is indicated within the bars. * p < 0.05 compared with the corresponding vehicle group (two-tailed Student’s t-test).

Figure 6

Effects of NLX-101 (0.16 mg/kg) and vehicle (Veh) on the concentration of BDNF (a), pAkt (b) and GluA1 (c) in the prefrontal cortex at 30 min, 1 h, 2 h and 6 h after its intraperitoneal administration. Results are expressed as mean ± SEM. Number of animals is indicated within the bars. * p < 0.05 compared with the corresponding vehicle group (two-tailed Student’s t-test).

Figure 7

Effects of NLX-101 (0.16 mg/kg) and vehicle (Veh) on the concentration of β-arrestin 1 (a) and β-arrestin 2 (b) in the prefrontal cortex at 30 min, 1 h, 2 h and 6 h after its intraperitoneal administration. Results are expressed as mean ± SEM. Number of animals is indicated within the bars.

Figure 8

Scheme of the intracellular signaling pathways involved in the antidepressant-like effects of NLX-101. NLX-101 preferentially activates 5-HT_1A receptors expressed in GABA interneurons, thus reducing their activity and inducing a disinhibition of glutamatergic neurons with the subsequent release of glutamate and dopamine. Glutamate would evoke a rapid (1) stimulation of AMPA receptors (AMPAR) localized to the plasma membrane of pyramidal cells, which would result in a rapid intracellular activation of CaMKII that would eventually activate (phosphorylate) ERK1/2 and mTOR pathways, thus inducing a rapid synthesis of PSD95 and p11. The binding of dopamine to D1 receptors (D1R) can also contribute to the expression of ERK1/2 through activation of protein kinase A. A delayed antidepressant mechanism (2) would involve the mTOR-induced synthesis of BDNF that would bind to its receptor, TrkB, followed by downstream activation of Akt and synthesis of GluA1. Abbreviations: AMPA, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid; BDNF, brain-derived neurotrophic factor; CaMKII, Ca²⁺/calmodulin-dependent protein kinase II; D1, dopamine D1 receptor; ERK1/2, extracellular-regulated kinase 1/2; mTOR, mammalian target of rapamycin; PI3K, phosphatidylinositol-3 kinase; TrkB, tropomyosin receptor kinase B; VDCC, voltage-dependent calcium channel. Illustration created with BioRender.com, accessed on 26 January 2022.